how soon after a new computer is released....

How soon after a new computer is released (say a powerbook) does Apple stop selling the older model on their website?

I am asking because I want to get a PB from Apple with the student discount. They may be releasing new ones in January and I'm not sure if I will be able to buy it before then and I do not want a new intel powerbook, just the kind they have now.

I have no inside info here, but I don't think a January release of PBs will have Intel chips. My understanding was that the intels weren't going to be released until the summer. My guess would be that the PowerMac would be the first to get them.